Defrost control apparatus



United States Patent O 3,962,619 DEFRSI CONTROL APPARATUS Luther I. .Inngemann and Lleyd G. Hupfer, Evansville,

Ind., assignors to Whiripoal Corporation, a corporation of Delaware Filed Dec. 9, 1%0, Ser. No. 75,009 '7 Ctaims. (Sl. 62-146) This invention relates to a defros-t control apparatus for a refrigerated member subject to icing.

In many types of equipment that include a refrigerated member subject to icing a heat exchange iluid such as air is forced in heat transfer contact with the refrigerated member in order to cool the fluid. It often occurs particularly when the refrigerated member is a coil or other type structure through which the iluid such as air is blown -that increased icing changes the air flow 'characteristics. Thus, when the air for example is drawn through the refrigerated member the air pressure on the low pressure side of the member drops because of restricted air flow. For the same reason when the air is blown through lthe refrigerated member the air pressure on the high pressure side of the member tends to increase also due to the restricted air flow.

In the present invention advantage is taken of these changes in fluid ow characteristics in order to initiate a defrosting operation. Because air flow changes in such a refrigerated member are not always due to increased icing, however, a more accurate defrost control apparatus is provided in this invention by employing a pair of variable means each variable independently of the other due to changing icing conditions with respect to the refrigerated member, a defrost actuating member for initiating defrosting, aid means operated only by joint operation of both of these variable means when each has reached a predetermined condition indicative of undesirable icing to cause operation of the defrost actuating member.

One of the features of this invention therefore is to provide an improved defrost control apparatus of the above 4type for a refrigerated member subject to icing.

Another feature of the invention is to provide such an apparatus in which defrosting is brough-t about or initiated only by the joint functioning of at least two independently variable means each independently affected by increased icing conditions and each operating at predetermined values or conditions to bring about the defrosting operation.

Other features and advantages of the invention will be apparent from the following description of one embodiment thereof taken in conjunction with the accompanying drawings. Of the drawings:

FIGURE 1 is a semi-diagrammatic view of an air conditioning system including a defrost control apparatus embodying the invention.

FIGURE 2 is a fragmentary view similar to the lefthand portion of FIGURE 1 illustrating the positions of certain parts of the apparatus during the defrosting operation.

FIGURE 3 is a diagrammatic view showing a portion of the wiring diagram `of the illustrated system.

In the embodiment shown in the drawings there is illustrated an air conditioning system including an evaporator 5 including the usual conduit 7 arranged in a back and forth continuous coil formation. One portion 8 of the conduit 7 extends outwardly of the evaporator 5 and exteriorly of an end iin 6. The evaporator 5 is provided with an outlet conduit 9 leading to a compressor 10 and an outlet conduit 11 leads from the compressor to an inlet indicated at 12 of a condenser 15. This condenser is also made up of back and forth passes of a conduit 13 to form a coil and is provided with heat transfer ns 14. From the outlet 16 side of the condenser 15 a con- ICC duit 17 leads through a capillary indicated diagrammatically at 19 and then through another conduit 20 to the inlet 21 of the evaporator 5.

The inner side of the evaporator 5 is enclosed by a shroud 26 which is open at its inner end to communicate with a blower 27 which includes a plurality of blades 28. A housing 29 surrounds the blower 27 with this housing being provided with an outlet (not shown) so that operation of the blower 27 causes air to be drawn through the coil of the evaporator 5, through the shroud 26 and expelled from the housing 29 as indicated by the broken lines on the left-hand side of FIGURE l.

A similar blower 35 is provided in a similar housing 36 communicating with a shroud 39 enclosing the inner side of the condenser 15. Operation of the blower 35 serves to draw air through the coil of the condenser 15 and to expel it from the housing 36 as indicated by the broken line arrows on the right-hand side of FIGURE l.

In order to operate the blowers 27 and 35 there is provided a single motor 40. Power to the compressor 10 and the motor 4t) is supplied as indicated in the circuit of FIGURE 3 by electric leads 43 and 44.

In order to control the power supply to the blower or fan motor 40 there is provided a switch 45 connected by a lead 46 in series with one side of the motor 40 and to the power line 44. The other side of the motor 40 .is connected to the power line 43 while the compressor 10 is connected between the lines 43 and 44 so that it is not affected by operation of the switch 45.

As ice tends to build up on the conduit or coil 7 of the evaporator 5, the partial vacuum within the shroud Z6 tends to lincrease. In order to use this increasing suction as an aid in initiating defrosting there is provided a pressure responsive device 5t arranged to be operated by the increasing suction within the shroud 26 due to this increased icing. This device 50 includes a housing made up of cooperating sides 51 and 52 that are spaced from an internal diaphragm 53 to provide chambers 54 and 55 on opposite sides of the diaphragm. The chamber 55 is operatively connected to the interior of the shroud 26 by means of a tube 56 so that the suction within the shroud 26 also produces suction in the chamber 55 which would of course tend to move diaphragm 53 to the right as viewed in FIGURE l. In order to permit relatively unretarded movement to the diaphragm 53 there is provided an opening `57 in the side 51 of the device 50.

At about the center of the diaphragm 53 there is provided an outwardly extending catch 58 slidably mounted Iwithin the device side 51 so as to be movable horizontally as viewed in FIGURE l upon movement of the diaphragm 53.

The switch 45 which is in series with the motor 40 is provided with a pair of spaced contacts 60 that are normally adjacent an arm 61 of the switch. This arm 61 is arcuately movable on a mounting bracket 62 about a pivot 63. The arm 61 carries an elongated contact 65 as shown in FIGURE l so that when the arm 61 is in closed position as shown in FIGURE l current flows from one side of the line 46 through a contact 60, the elongated contact 65, the other contact 66 and through the other side of the line 46. Therefore so long as the switch arm 61 is in the position shown in FIGURE 1 current flows to the motor 40 and ythe two blowers 27 and 35 are rotated to cause air flow as indicated.

Spaced beneath the switch arm 61 is an inflatable and deilatable bellows 66 which is connected by means of a capillary 67 to a temperature `sensing device 90 which includes la sensing bulb 91 in thermal contact with the evaporator coil portion 8. In the embodiment illustrated the free end of the bellows 66 moves substantially vertically and is attached to a finger 68 whose upper end bears against the bottom of the switch arm 61. As can be seen in the drawings, the fixed contacts 6% are positioned on the side of the arm 61 opposite to the finger 68.

When the Sair conditioner is operating normally, the parts are in the position shown in FIGURE 1. When ice begins to build up on the conduit 7 and fins 6 of an evaporator S because the operating surface temperature of the evaporator drops below freezing and is below the wet bulb temperature, the air pressure within the shroud 26 is reduced to a greater than normal suction. Thus these are two independent variables that are each indicative of an undesirable icing condition on the evaporator. When the suction reaches a predetermined value indicative of undesirable ice formation on the evaporator conduit 7, the diaphragm 53 is moved a sufficient distance, due to the increased suction, to release the catch from the end of the arm 61. The temperature sensing device 90 is set to begin the collapse of the bellows 66 when the temperature in the conduit 7 reaches approximately 32 F. This collapse of the bellows 66, which retracts the finger 68, and the movement of the catch 58 to the right permit gravity action `on the switch arm 61 to lower the arm about the pivot 63 and break the electrical circuit through the contacts 663-65. This breaks the circuit to the motor 4) as illustrated in FIGURES 2 and 3 but does not affect the operation of the compressor 10. The resulting stopping of the blower 35 greatly reduces the cooling of the refrigerant in the condenser 15. The temperature of the refrigerant therefore begins to rise not only in the condenser but also throughout the refrigerant system including the evaporator 5. As soon as this gradually heating refrigerant exceeds the freezing temperature within the evaporator the ice of course begins to melt thereby defrosting the evaporator. When the temperature of the refrigerant in the evaporator 5 reaches a. predetermined above freezing temperature indicating that all ice has been melted the pressure within the temperature sensing device 9) increases thereby causing the bellows 66 to expand and raise the switch arm 61 thereby reenergizing contacts 60-65 to again energize motor 40 which drives blowers 27 and 35.

In the meantime as soon as the motor 40 has stopped operating at the initiation of the deicing period as mentioned air pressure within the shroud 26 rises to a normal level due to the blower 27 no longer operating. This serves to return the diaphragm 53 and thus the catch 58 to their normal positions as illustrated in FIG- URE 1. As can be seen in the drawings the outer end of the catch 58 is inclined so that the outer end of the switch arm 61 can move past the extended catch 53. At the conclusion of these actions the lair conditioner resumes its normal operation.

As can be seen from the above description, the initiation of the defrosting cycle requires the joint operation of two independently operable variable means, each variable by a condition that may indicate icing on the evaporator. Thus, in the illustrated embodiment these two variable means are (1) the increasing suction within the evaporator shroud 26 and (2) the drop in temperature within the evaporator coil 7. With the structure of this invention either of these two variables alone is sutiicient to initiate the defrosting cycle as it requires the operation of both jointly. This is an important feature as either of these variables may function to give a false indication under circumstances when very little or no ice is present. Thus, if only the suction actuated device were used, suction could be increased by accidental blockage `of the air passage through the evaporator 5, as for example, by a curtain engaging the upstream side of the evaporator. Similarly the temperature actuated device 90 if used alone could give a false signal since it is possible for the evaporator 7 to be operating -at a sub-freezing temperature without the accumulation of i ice or frost if the wet bulb temperature of the air being conducted over the evaporator surface is lower than the surface temperature of the evaporator.

Having described our invention as related to the embodiment shown in the accompanying drawings, it is our intention that the invention be not limited by any of the details of description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

We claim:

1. Defrost control apparatus for use in a refrigeration apparatus having a member subject to icing and means for defrosting the member, comprising: a first variable means responsive to a first condition indicative of icing of said refrigerated member; a second variable means operable independently of said first variable means and responsive to a different, non-thermal second condition indicative of icing of said refrigerated member; and actuating means for operating the defrosting means, said actuating means being arranged to be operated only as the result of a preselected joint arrangement of said first and second variable means in which arrangement each variable means is in a condition indicative of undesirable icing.

2. The defrost control of claim 1 wherein said actuating means includes electrical switch means.

3. Defrost control apparatus for a refrigerated member subject to icing and past which iiuid flows in heat transfer relationship, the iiuid flow being variable due to variable icing conditions, comprising: a first variable means variable by said variable fluid flow; a second variable means variable by temperature changes in said refrigerated member; a defrost actuating member operable to initiate defrosting; and means operated by joint operation of both said variable means only when each has reached a predetermined condition indicative of undesirable icing to thusly operate said defrost actuating member.

4. Defrost control apparatus for an evaporator coil subject to icing and through which air flows in heat transfer relationship, the air flow being Variable due to variable icing conditions, comprising: an air pressure responsive variable means variable by said variable air flow; a temperature responsive variable means variable by temperature changes in said evaporator coil; a defrost actuating member operable to initiate defrosting; and means operated by joint operation of both said variable means only when each has reached a predetermined condition indicative of undesirable icing to thusly operate said defrost actuating member.

5. Defrost control apparatus for an evaporator coil subject to icing, comprising: air moving means for drawing air through said coil from an upstream side through a downstream side; an air pressure responsive means communicating with said downstream side and variable with pressure drop therein indicative of icing on said coil; a temperature responsive means variable with refrigerant temperatures including below freezing temperatures within said coil, each of said responsive means being indicative of undesirable icing conditions on said coil when such exist; a defrost actuating member operable to initiate defrosting; and means operated by joint operation of both said responsive means only when each has reached a predetermined condition indicative of said undesirable icing to thusly operate said defrost actuating member.

6. Defrost control apparatus for an evaporator coil subject to icing, comprising: electrically operated air moving means for drawing air through said coil from an upstream side through a downstream side including an electrical circuit; an electrical switch in said circuit; an air pressure responsive means communicating with said downstream side and variable with pressure drop therein indicative of icing on said coil; a temperature responsive means variable with refrigerant temperatures including below freezing temperatures within said coil, each of said responsive means being indicative of undesirable icing conditions on said coil when such exist; and means operated by joint operation of both said air pressure responsive means and said temperature responsive means only when each has reached a predetermined condition indicative of said undesirable icing to cause opening of said switch to inactivate said air moving means thereby to bring about defrosting of said coil.

7. Refrigeration apparatus, comprising: an evaporator coil subject to icing; a condenser coil; fluid means connecting said coils in a uid refrigerant flow series circuit; means for causing refrigerant ow through said series; electrically operated means for forcing air through each of said Icoils including an electrical circuit; an electrical switch in said circuit; an air pressure responsive means variable with air pressure drop through said evaporator coil indicative of icing on said coil; a temperature responsive means variable with refrigerant temperature including below freezing temperatures within said evaporator coil, each of said responsive means being indicative of undesirable icing conditions on said evaporator coil when such exist; and means operated by joint operation of both said air pressure responsive means and said temperature responsive means only when each has reached a predetermined condition indicative of said undesirable icing to cause opening of said switch to inactivate said air moving means thereby to bring about defrosting of said evaporator coil due to inadequate cooling of refrigerant in said condenser coil of said circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,428,667 Henrquez Oct. 7, 1947 2,728,197 Ellenberger Dec. 27, 1955 2,744,389 Raney ...t May 8, 1956 2,975,611 Pietsch Mar. 2l, 1961 

